Method of transmitting feedback information using an extended subheader

ABSTRACT

A method of transmitting feedback information is disclosed. More specifically, a mobile station (MS) receives a Protocol Data Unit (PDU) which includes a Medium Access Channel (MAC) header from a base station (BS). Thereafter, the MS determines from the received MAC header whether an extended subheader group appears after the MAC header, and also identifies a feedback request extended subheader from the extended subheader group. Lastly, the MS transmits the feedback information according to the feedback request extended subheader.

This application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2004-112927, filed on Dec. 27, 2004, Korean Application No. 10-2005-000930, filed on Jan. 5, 2005, and U.S. Provisional Application No. 60/663,347 filed on Mar. 17, 2005, which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of transmitting feedback information, and more particularly, to a method of transmitting feedback information using an extended subheader.

2. Discussion of the Related Art

FIG. 1 is an example illustrating a structure of a Medium Access Control (MAC) Protocol Data Unit (PDU). As illustrated in FIG. 1, the MAC Management PDU includes a MAC Header 11, a Management Message Type 12, and a MAC Management Payload 13. Furthermore, a Bandwidth Request PDU is used by each user to dynamically request a necessary bandwidth for transmitting uplink data. The Bandwidth Request PDU is special in that it only includes the bandwidth request header and nothing else including a payload.

FIG. 2 illustrates a structure of the MAC PDU of FIG. 1. More specifically, if a MAC PDU is formed without packing or fragmenting a MAC Service Data Unit (SDU), as illustrated in FIG. 2, a MAC PDU does not included a packing subheader or a fragmentation subheader.

FIG. 3 illustrates another example of a structure of a MAC PDU. As illustrated in FIG. 3, a MAC SDU 31 is fragmented to be included in forming two or more MAC PDUs 30 a and 30 b. In forming the MAC PDUs 30 a and 30 b, fragmentation subheaders 34 a and 34 b are attached behind the MAC headers 33 a and 33 b, respectively. Moreover, MAC SDUs 35 a and 35 b are attached behind the fragmentation subheaders 34 a and 34 b, respectively, to form MAC PDUs 30 a and 30 b.

FIG. 4 is yet another example illustrating a structure of a MAC PDU. In FIG. 4, a MAC PDU is formed by packing two or more MAC SDUs (e.g., MAC SDU #1 41 a and MAC SDU #2 41 b). These MAC SDUs 44 and 46 are attached behind packing subheaders 43 and 46, respectively. Here, the MAC PDU has a MAC header 42 in front and more specifically, in front of the packing subheader 43.

As described above, when the MAC SDU is fragmented or packed, fragmentation subheader or packing subheader is attached to the respective MAC PDU(s). As such, the MAC PDU can be classified in its respective units and according to frame numbers.

In the conventional art, only the methods related to fragmenting and packing are available. In other words, the conventional art does not include a MAC PDU structure having various expanded subheaders.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of transmitting feedback information using an extended subheader that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of transmitting feedback information.

Another object of the present invention is to provide a method of receiving feedback information.

A further object of the present invention is to provide a system for transmitting and receiving feedback information.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a method of transmitting feedback information includes a mobile station (MS) which receives from a base station (BS) a Protocol Data Unit (PDU) which includes a Medium Access Channel (MAC) header. Thereafter, the MS determines from the received MAC header whether an extended subheader group appears after the MAC header, and also identifies a feedback request extended subheader from the extended subheader group. Lastly, the MS transmits the feedback information according to the feedback request extended subheader.

In another aspect of the present invention, a method of transmitting feedback information includes a base station (BS) which transmits a Protocol Data Unit (PDU) which includes a Medium Access Channel (MAC) header which indicates an existence of an extended subheader group. Here, the extended subheader group includes a feedback request extended subheader. Thereafter, the BS receives the feedback information transmitted from a mobile station (MS).

Yet in another aspect of the present invention, a system for transmitting and receiving feedback information includes a base station (BS) which transmits a Protocol Data Unit (PDU) which includes a Medium Access Channel (MAC) header which indicates whether an extended subheader group appears after the MAC header. Here, the extended subheader group indicates a feedback request extended subheader. The system also includes a mobile station (MS) which receives the PDU and then determines from the MAC header whether the extended subheader appears after the MAC header. Thereafter, the MS determines from the MAC header whether an extended subheader group appears after the MAC header. Moreover, the MS identifies a feedback request extended subheader from the extended subheader group. Lastly, the MS transmits the feedback information according to the feedback request extended subheader.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings;

FIG. 1 s an example illustrating a structure of a Medium Access Control (MAC) Protocol Data Unit (PDU);

FIG. 2 illustrates a structure of the MAC PDU of FIG. 1;

FIG. 3 illustrates another example of a structure of a MAC PDU;

FIG. 4 is yet another example illustrating a structure of a MAC PDU;

FIG. 5 illustrates an example of a MAC header;

FIG. 6 is another example illustrating a MAC header;

FIG. 7 depicts an example of a MAC PDU;

FIG. 8 is a diagram depicting a structure of an extended subheader group; and

FIG. 9 is an example of an Extended Subheader Format (ESF).

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 5 illustrates an example of a MAC header. As illustrated in FIG. 5, the MAC header includes a ‘type’ field represented by 6 bits. Moreover, the ‘type’ field can express six (6) different types of subheaders depending on the bitmap type. These different types of subheaders can be attached behind the MAC header, and a specific type of the subheader can be indicated in the ‘type’ field, This type field indicates six (6) types of subheaders, and each subheader has a size of 2 bytes.

Table 1 shows an example of six (6) types of subheaders. TABLE 1 Type bit Value #5 Most Mesh subheader Significant 1 = present, 0 = absent Bit (MSB) #4 ARQ Feedback Payload 1 = present, 0 = absent #3 Extended Type Indicates whether the present Packing or Fragmentation Subheaders, is Extended 1 = Extended 0 = Not Extended. Applicable to connections where ARQ is not enabled #2 Fragment subheader 1 = present, 0 = absent #1 Packing subheader 1 = present, 0 = absent #0 Least Downlink: FAST-FEEDBACK Allocation subheader Significant Uplink: Grant Management subheader Bit (LSB) 1 = present, 0 = absent

As shown in Table 1, there are six types of subheaders, represented by a most significant bit (MSB) #5 to a least significant bit (LSB) #0. Each type of subheader can be indicated as being present or as being absent. More specifically, the type bit of ‘1’ or ‘0’ indicates presence or absence of the particular subheader, respectively.

For example, if the ‘type’ bit #5 is indicated as ‘1,’ the MAC PDU includes a mesh subheader. That is, in a mesh mode, each mobile station (MS) is given a Node identification (Node ID) so that each MS can be identified. To this end, the mesh subheader can be used to provide Node ID to each MS. If the ‘type’ bit #4 is indicated as 1, then the MAC PDU includes a subheader for an Automatic Repeat Request (ARQ). If the ‘type’ bit #3 is indicated as 1, then the MAC PDU includes an extended packing subheader or an extended fragmentation subheader. If the ‘type’ bit #2 and the ‘type’ bit #1 are each indicated as ‘1,’ a packet PDU corresponding to a user are mapped to a MAC SDU payload. Moreover, a MAC PDU is formed by having a MAC header and a Cyclic Redundancy Check (CRC) attached thereto.

Lastly, an application of the bit of the ‘type’ bit #0 is different for an uplink transmission and for a downlink transmission. If the ‘type’ bit #0 is indicated as ‘1,’ the MAC PDU includes a fast-feedback allocation subheader. Here, the fast-feedback allocation subheader is positioned at the end of all subheaders. In order to receive a feedback value from the MS, the fast-feedback allocation subheader is used to allocate resource(s) in a fast feedback channel (e.g., Channel Quality Indication Channel) and the type of feedback information.

An example of a fast-feedback allocation subheader is presented in Table 2. TABLE 2 Syntax Size Notes FAST-FEEDBACK allocation Subheader { Allocation offset 6 bits Feedback type 2 bits 00: Fast DL measurement 01: Fast MIMO feedback antenna#0 10: Fast MIMO feedback antenna#1 11: MIMO mode permutation mode feedback }

As depicted in Table 2, the fast-feedback allocation subheader uses an ‘allocation offset’ to allocate a Channel Quality Indication Channel (CQICH), which is indicated by a fast feedback channel Information Element (IE), for transmitting feedback information. Here, the allocation of CQICH can be represented in slots. In addition, a type of feedback information can be selected via the ‘feedback type.’ After the MS receives the fast-feedback allocation subheader, the MS can use the feedback value to request for a change to a Multi Input Multi Output (MIMO) mode or to a permutation mode,

For an uplink, if the ‘type’ bit #0 is indicated as ‘1,’ the MAC PDU includes a Grant Management subheader. The Grant Management subheader is used to deliver information related to managing the uplink resources. Moreover, the use of the Grant Management subheader can vary depending on a subheader type. Based on the type of service, an allocation request for bandwidth using a piggyback request, bandwidth stealing scheme, and a polling scheme.

As illustrated in FIG. 5, the MAC header includes two reserved bits, each having 1 bit length. Here, any one of the two reserved bits can be used to include information of an enhanced fast-feedback allocation subheader. In other words, a reserved bit can be used to indicate whether an enhanced fast-feedback allocation subheader is attached.

If the reserved bit is indicated as 1, the MAC header includes information of existence of the enhanced fast-feedback allocation subheader, and alternatively, if the reserved bit is indicated as ‘0,’ the MAC header does not include any information on the enhanced fast-feedback allocation subheader.

Table 3 shows an example of an enhanced fast-feedback allocation subheader. TABLE 3 Size Syntax (bits) Notes Enhanced Fast-feedback allocation subheader{  Allocation type 1 0 = Use Fast-Feedback channel 1 = Use Feedback MAC header  If allocation  type == 0 {   Allocation offset 6 Represented in slots, starting frame offset value for Fast-Feedback channel   CQICH_num 4 Number of CQICH slot(s) to be used   Feedback type 3 #0 least significant bit(LSB) ? Fast DL measurement #1 - Fast MIMO feedback, antenna #0 #2 - Fast MIMO feedback, antenna #1 #3 - Fast MIMO feedback, antenna #2 #4 - Fast MIMO feedback, antenna #3 #5 - MIMO mode and Permutation mode feedback #6-#8 reserved   Frame offset 2 BS indicates starting frame  } else {   UIUC 4   Duration 4 MS indicates starting frame   Feedback type 4 Refer to Table 4   Frame offset 3 }

According to Table 3, the enhanced fast-feedback allocation subheader transmits a data packet to the MS. In addition, the enhanced fast-feedback allocation subheader requests for feedback on information pertaining to the transmission channel and weight value(s) of the antennas. Here, additional information can be requested such as a method of transmitting the feedback information.

In Table 3, an ‘allocation type’ field can be used to select a method of transmitting feedback information. For example, if the ‘allocation type’ field is indicated by ‘0,’ the MS uses the fast feedback channel to transmit the feedback information. In such a case, an ‘allocation offset’ field is used to indicate the location of the fast feedback channel, and a ‘CQICH_num’ field is used to determine a number of slots to be used transmit the feedback information.

Moreover, a ‘feedback type’ field is used to indicate the contents of the feedback information. For example, if a BS uses two antennas, the BS can request for weight values corresponding to a first antenna and a second antenna while allocating two slots. Then the MS can send the weight value for the first antenna and the weight value for the second antenna using the allocated slots.

Furthermore, a ‘frame offset’ field can be used to provide information as to when the MS should send the feedback information. That is, after the MS receives the subheader, the MS can send the feedback information after a specified period or after a specified number of frames.

Alternatively, if the ‘allocation type’ field is indicated by ‘1,’ the MS uses the MAC header to transmit the feedback information. Here, a ‘duration’ field is used to provided information regarding allocated wireless resource in the uplink, and a ‘feedback type’ is used to indicate the type of feedback information.

Table 4 is an example illustrating feedback information corresponding to ‘feedback type’ field value. TABLE 4 Feedback Type Feedback contents Description 0b0000 Set as described in table 296d MIMO mode and permutation feedback 0b0001 DL average CQI (5bits) 5 bits CQI feedback 0b0010 Number of index L(2bits) + MIMO MIMO coefficients coefficient (5bits. 8.4.5.4.10.6) feedback 0b0011 Preferred-DIUC(4bits) Preferred DL channel DIUC feedback 0b0100 UL-TX-Power(7bits) UL transmission power 0b0101 Preferred DIUC(4bits) + UL-TX- PHY channel feedback Power(7bits) + UL-headroom(6bits) 0b0110 Number of bands, N(2bits) + N occurrences CQIs of multiple AMC of ‘band index(6 bits) + CQI (5bits) bands 0b0111 Number of feedback types, 0(2bits) + O Multiple types of feedback occurrences of ‘feedback type(4bits) + feedback content (variable)’ 0b1000-0b1111 Reserved for future use

As described above, if the ‘allocation type’ field is indicated by ‘1,’ the MS receives the enhanced fast-feedback allocation subheader and uses the allocated uplink wireless resources to transmit the feedback information via the MAC header.

FIG. 6 is another example illustrating a MAC header. As illustrated in FIG. 6, the MAC header includes an Extended Subheader Format (ESF) field to further express an extended subheader group. That is, if the ESF field value is set to ‘1,’ an extended subheader group is provided between the MAC header and six types of subheaders (immediately after the MAC header), which is expressed via a ‘type’ field, Alternatively, the extended subheader group can appear between the subheaders and a payload. Hereafter, a term ‘extended subheader’ may be used interchangeably as a term ‘extended subheader group.’

FIG. 7 depicts an example of a MAC PDU. As show in this figure, the MAC PDU includes a MAC header 71, an ESF 72, subheaders 73, a payload 74, and a CRC 75. The ESF 72 can be located between the MAC header 71 and the subheaders 73, and the length of the ESF 72 can be determined based on a number of attached subheaders. Alternatively, the ESF 72 can appear or attached behind the subheaders 73.

The BS can set the value of the ESF field as ‘1’ in the MAC header so that the MS can be notified as to the existence of the ESF between the MAC header and the subheaders. Furthermore, the ESF should not be encrypted; however, the MS can perform the error detection operation by using the CRC located at the end of the PDU.

FIG. 8 is a diagram depicting a structure of an extended subheader group. As depicted in FIG. 8, the extended subheader group consists of an extended subheader lengths field 81 for providing a total length of the extended subheader group, a reserved bit field 82, an extended subheader type field 83, and an extended subheader body 84. Preferably, the extended subheader lengths field should be represented in 8 bits, and the total length of the extended subheader is represented in bytes. Here, the total length can be represented by maximum of 2⁷ bytes. Furthermore, there can be up to 128 types of extended subheaders.

Table 5 is an example of an extended subheader types. TABLE 5 ESF Type value Name Length (bytes) 0 New Extended subheader_1 1 1 New Extended subheader_2 2 Bits 2-127 Reserved

Here, Table 5 illustrates addition of two extended subheaders. That is, based on the extended subheader type field 83, a type corresponding to ‘0’ has an extended subheader_1 having a length of one (1) byte while a type corresponding to ‘1’ has an extended subheader_2 having a length of two (2) bytes. Depending on the type, the extended subheader can be classified into whether the subheader is for uplink or downlink transmission. For example, a subheader used in the uplink is formed at the MS and transmitted to the BS, and if the MS receives this subheader, the MS disregards it.

FIG. 9 is an example of a format of an ESF. Here, refer to FIGS. 7 and 8 as well as Table 2. In FIG. 9, the MAC PDU includes the extended subheader group, and an extended subheader length field 91 is used to indicate a total length of the subheader(s). In this figure, the total length of the subheaders is six (6) bytes.

In detail, a new extended subheader_1 includes a reserved bit 92 and an extended subheader type 93. Here, the extended subheader type is ‘0’ and has a length equaling 1 byte. Moreover, a body 94 of the extended subheader contains information of a subheader represented by type ‘0’ and having a length of 1 byte.

Furthermore, a new extended subheader_2 includes a reserved bit 95 and an extended subheader type 97. Here, the extended subheader type is ‘1’ and has a length of 2 bytes. In a body 97 of the extended subheader_2, different from the new extended subheader_1, there are two subheaders having the length of 2 bytes.

Table 6 is an example of a downlink extended subheader attached to the MAC PDU. TABLE 6 ESF Type value Name Length 0 SDU_SN Extended subheader 1 1 DL Sleep control Extended subheader 3 2 Feedback request Extended subheader 3 3 PDU SN(short) Extended subheader 1 4 PDU SN(long) Extended subheader 2 Bits# 5-127 Reserved

As shown in Table 6, at least one subheader is attached to the MAC PDU before being transmitted. For example, if the ESF type field indicates a value of ‘00000010,’ a feedback request extended subheader, having a length of 3 bits, is attached to the MAC PDU.

Table 7 is another example of an uplink extended subheader group attached to the MAC PDU. TABLE 7 ESF Type value Name Length 0 MIMO mode feedback Extended subheader 1 1 UL Tx power report Extended subheader 1 2 Mini-Feedback report Extended subheader 2 3 PDU SN(short) Extended Extended 1 subheader 4 PDU SN(long) Extended subheader 2 Bits# 5-127 Reserved

As shown in Table 7, at least one subheader is attached to the MAC PDU before being transmitted. For example, if there is a request for MIMO mode change, a MIMO mode feedback extended subheader is transmitted after a desired mode is selected.

Table 8 is an example of a feedback request extended subheader format from an uplink extended subheader. TABLE 8 Size Name (bits) Description UIUC 4 Feedback type 4 Refer to Table 4 OFDMA 6 The offset is relevance to the Allocation Start Symbol offset Time field given in the UL-MAP message. Subchannel 6 The lowest index subchannel used for carrying offset the burst, starting from Subchannel 0. No. slot 3 The number of slots allocated for the burst Frame 1 Indicate to start reporting at the frame. If F == 0, offset(F) the allocation applies to the UL subframe two frames ahead of the current frame. If F == 1, for frames ahead of the current frame.

As depicted in Table 8, a feedback request extended subheader format can be 3 bytes in length. If the feedback request extended subheader format is transmitted to the MS, the MS transmits feedback information according to the contents of the feedback request extended subheader using the allocated uplink wireless resource. In addition, an ‘OFDMA symbol offset’ field and a ‘subchannel offset’ field provide a location of the uplink resource for feedback information. Moreover, a ‘No. slot’ field indicates a number of slots allocated for the burst or a number slots to be used from a designated location. Here, a method of encoding for the feedback information is determined using an Uplink Interval Usage Code (UIUC). Lastly, a ‘frame offset’ field provides a starting frame for transmitting feedback information, where the starting frame is a frame at which the feedback information is to be begin transmitting.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1-24. (canceled)
 25. A method of communicating between entities in a mobile communication system, the method comprising: receiving a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; determining from a field in the MAC header whether at least one additional field is present in the MAC header; and transmitting information in response to the contents of the at least one additional field, wherein the at least one additional field comprises information related to at least one of uplink and downlink communication resources.
 26. The method of claim 25, wherein determining whether at least one additional field present in the MAC header comprises determining the status of at least one bit in the MAC header field.
 27. The method of claim 25, further comprising identifying a type of the at least one additional field.
 28. The method of claim 25, wherein the at least one additional field is an optional field.
 29. A method of communicating between entities in a mobile communication system, the method comprising: receiving a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; determining from a field the MAC header whether at least one optional field is present in the MAC header; identifying a type of the at least one optional field; and transmitting information in response to the contents of the at least one optional field, wherein the at least one optional field comprises information related to at least one of uplink and downlink communication resources.
 30. The method of claim 29, wherein determining whether at least one optional field present in the MAC header comprises determining the status of at least one bit in a non-optional MAC header field.
 31. A method of communicating between entities in a mobile communication system, the method comprising: generating a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; and transmitting the PDU, wherein a field in the MAC header comprises an indication that at least one additional field is present in the MAC header, the at least one additional field comprising information related to at least one of uplink and downlink communication resources.
 32. The method of claim 31, wherein the indication that at least one additional field is present in the MAC header comprises at least one bit in the MAC header field.
 33. The method of claim 31, further comprising identifying a type of the at least one additional field.
 34. The method of claim 31, wherein the at least one additional field is an optional field.
 35. A method of communicating between entities in a mobile communication system, the method comprising: generating a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; and transmitting the PDU, wherein a field in the MAC header comprises an indication that at least one optional field is present in the MAC header, the at least one optional field comprising information related to at least one of uplink and downlink communication resources.
 36. The method of claim 35, wherein the indication that at least one additional field is present in the MAC header comprises at least one bit in a non-optional MAC header field.
 37. The method of claim 35, further comprising identifying a type of the at least one optional field.
 38. A system for communicating between entities in a mobile communication system, the system comprising: a transmitting unit adapted to generate and transmit a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header, a field in the MAC header comprising an indication that at least one additional field is present in the MAC header, the at least one additional field comprising information related to at least one of uplink and downlink communication resources; and a receiving unit adapted to receive the Protocol Data Unit (PDU), determine from the MAC header field whether the at least one additional field is present in the MAC header and transmit information in response to the contents of the at least one additional field.
 39. The method of claim 38, wherein the indication that the at least one additional field is present in the MAC header comprises at least one bit in the MAC header field.
 40. The method of claim 38, further comprising identifying a type of the at least one additional field.
 41. The method of claim 38, wherein the at least one additional field is an optional field.
 42. A system for communicating between entities in a mobile communication system, the system comprising: a transmitting unit adapted to generate and transmit a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header, a field in the MAC header comprising an indication that at least one optional field is present in the MAC header, the at least one optional field comprising information related to at least one of uplink and downlink communication resources; and a receiving unit adapted to receive the Protocol Data Unit (PDU), determine from the MAC header whether the at least one optional field is present in the MAC header, identify a type of the at least one optional field and transmit information in response to the contents of the at least one optional field.
 43. The method of claim 42, wherein the indication that the at least one optional field is present in the MAC header comprises at least one bit in a non-optional MAC header field.
 44. A method of communicating between entities in a mobile communication system, the method comprising: receiving a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; determining from a field in the MAC header whether at least one additional field is present; and transmitting information in response to the contents of the at least one additional field, wherein the at least one additional field comprises information related to at least one of uplink and downlink communication resources.
 45. A method of communicating between entities in a mobile communication system, the method comprising: generating a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header; and transmitting the PDU, wherein a field in the MAC header comprises an indication that at least one additional field is present, the at least one additional field comprising information related to at least one of uplink and downlink communication resources.
 46. A system for communicating between entities in a mobile communication system, the system comprising: a transmitting unit adapted to generate and transmit a Protocol Data Unit (PDU) including a Medium Access Channel (MAC) header, a field in the MAC header comprising an indication that at least one optional field is present, the at least one optional field comprising information related to at least one of uplink and downlink communication resources; and a receiving unit adapted to receive the Protocol Data Unit (PDU), determine from the MAC header whether the at least one optional field is present in the MAC header, identify a type of the at least one optional field and transmit information in response to the contents of the at least one optional field. 